By the title of this article you are probably thinking that Andrew Johnson was impeached. Many people think that he was just because of the title, but he was not impeached. He was tried for impeachment, but was acquitted by one vote.
Johnson's hearing for impeachment was on March 13,1868. Johnson was tried for impeachment because of many reasons. President Johnson obeyed the letter of the Reconstruction laws, but he was really against them. He chose people who liked the ex-confederates to serve as south military commanders. Johnson opposed a law passed by congress. This law was passed in 1867. The law challenged the President's power. In this law the President could not fire members of the cabinete, without the senate's approval.
To test this law, Johnson fired secretary of war, Edwin Stanton, in February 1868. Three days after, the House of Representatives voted to impeach him. They accused him of improper conduct while in office.
The problem between the president and the congress went past the 1867 law. The congress thought if they removed him from office, that would strengthen the reconstruction of the south.
Other things happened that led to Johnson's impeachment hearing. Most members of congress wanted to impeach him because they thought he was getting in the way of congress's plan of Reconstruction.
In a case of impeachment, the senate acts as the jury. Before the President can be impeached, two-thirds of a vote is needed. Johnson was acquitted, because the senate was short one vote.